1. Field of the Invention
This invention is directed to vaccines and there preparation from organisms taxonomically similar to the infective organism.
2. Description of the Prior Art
Immunotherapy with respect to infectious organisms has generally followed the theory of using either the organism itself or some intermediate state in its development as the basis for production of an immunizing vaccine. In this regard, the art is replete with examples of the effectiveness of this approach. For instance, immunization of chickens against cecal coccidiosis by establishing a controlled subclinical infection (U.S. Pat. No. 3,147,185); non-living vaccine produced by incubation of third-stage nematode larvae into the histotrophic stages (U.S. Pat. No. 3,395,218 and German Auslegesschrift No. 1,160,139); canine hookworm vaccine comprising a physiologically acceptable aqueous vehicle containing attenuated premigratory live hookworm larvae (U.S. Pat. No. 3,657,415); an Ascaris suum vaccine comprising sonicated third-stage larvae, sonicated second stage larvae, larvae hatching fluid and second-stage larval culture fluid (U.S. Pat. No. 3,676,547); an antigen preparation for immunoprecipitin diagnostic testing for Chagas' disease, caused by Trypanosoma cruzi, comprising purified, water-soluble antigen obtained from tissue culture of Trypanosoma cruzi to essentially only the trypomastigote and amastigote growth stages (U.S. Pat. No. 3,911,097); vaccine comprising a live, but attenuated, metazoan endoparasite which is pathogenic to domestic animals and is a nematode, trematode or cestode in the form of eggs or a premigratory or a migratory immature form (British Pat. No. 819,830 and Canadian Pat. No. 602,465); a vaccine comprising a metazoan or protozoan endoparasite, which elicits an immune response in the host, attenuated with a sub-lethal dose of ultraviolet radiation (British Pat. No. 902,760) and a vaccine comprising an antigen of Schistosoma mansoni separated from a development stage of the parasite (German Offenlegungsschrift No. 2,742,835). Additionally, a vaccine for canine hookworm has been produced which comprises a physiologically acceptable aqueous vehicle containing premigratory live hookworm larvae of a hookworm species which is specific to cats (British Pat. No. 1,277,134).
However, a need continues to exist for the preparation of vaccines against infectious organisms, which are either difficult or impossible to culture, in vitro, on a commercially practical scale. Exemplary of infectious organisms which cannot be readily cultured, in vitro, on a commercial scale are Ichthyophthirius multifiliis and Cryptocaryon irritans.
Ichthyophthirius multifilius and Cryptocaryon irritans are some of the most damaging parasites of warm water and salt water fish, respectively, and some of the most difficult to control. Experimental immunization of catfish with Ichthyophthirius multifiliis has been reported (Becker et al, "Some Host Response of White Catfish to Ichthyophthirius multifiliis Fouquet", Proc. 18th Ann. Conf. S.E. Assoc. Game and Fish Comm., 1964). Additional studies have shown that channel catfish injected intraperitoneally with vaccine prepared from the ground trophozoites, with and without Freund's adjuvant, survived challenge whereas control suffered 100% mortality after seven days (Areerat, S., "The Immune Response of Channel Catfish, Ictalurus punctatus (Rafinesque) to Ichthyophthirius multifiliis", Masters Thesis, Auburn University, Auburn, Ala. (1974)).
No known method exists for growing the protozoans Ichthyophthirius multifiliis and Cryptocaryon irritans, in vitro. Both Ichthyophthirius multifiliis and Cryptocaryon irritans are obligate parasites, the infective tomites must penetrate a host within 24-48 hours or perish. For this reason, maintenance of the parasites requires continual passage to susceptible hosts. Therefor, the accumulation of sufficient antigen to immunize large numbers of fish is very time-consuming and impractical.
Ichthyophthirius multifiliis and Cryptocaryon irritans are devastating parasites because they have a high morbidity and mortality. The diseases affect not only food fish, including trout, salmon, catfish, carp, eel, tuna, and bonita, but also ornamental fish. At present, chemical treatments are the only practical way of controlling the disease. These treatments including malachite green, formalin, methylene blue, potassium permanganate and others are not approved for use on food fish by the USDA.
Furthermore, malachite green, the most effective treatment, may soon be banned from use on any fish. Because of the limitations of chemotherapy, immunotherapy may be the only successful and practical approach to controlling these diseases.
A need therefore, continues to exist for a vaccine to immunize fish from the ravages of Ichthyophthirius multifiliis and Cryptocaryon irritans which can be readily produced on a scale suitable for aquacultural operations.